SOLVED — How Forensic Scientists Analyze Crime Scenes: Part 1 — Fingerprints

5 min readApr 16, 2023

At this point, TV shows revolving around solving crimes have cemented their position in pop culture. From “Criminal Minds” to “CSI: Crime Scene Investigation”, these shows have brought the stories of those who help to bring criminals to justice (and just as importantly, exonerate the innocent) to the public’s attention, albeit somewhat dramatized.

Some of the most important yet widely overlooked people responsible for achieving these goals are Forensic Scientists. Forensics can be defined as scientific tests and methodology used on samples of evidence collected at a crime scene to be used in court and to enforce the law. They help law enforcement determine the details of a crime and who the perpetrator was. With over 15400 Forensic Scientists in the United States alone, it is a position in very high demand, and for good reason.

But how exactly are Forensic Scientists able to come these conclusions? In this series, we will look at the pieces of evidence that Forensic Scientists analyze and what they look for. First up are fingerprints!

Background and Myth-Busting

Fingerprints are one of the earliest features to form, when a baby is in the womb at the 6-to-10-week mark, with volar pads forming on their fingers and toes. At the 24-week mark, fingerprints fully develop. However, before we move on, it’s important to bust two myths.

Fingerprints can change throughout your life: This is NOT true.
Identical twins have the same fingerprints: This is also NOT true, so you don’t have to worry about one twin being accused of another’s crime!

History

The following is a recording of a few of the most important events throughout history related to fingerprints.

In 3300 BC, fingerprints were widely used in the Indus Valley. They were placed on clay tablets and seals for identification purposes.
In 200 BC China, fingerprints were used to investigate burglaries.
In 800, clerks in China used inked fingerprints as a business seal or signature.
In 1100–1200, a Chinese novel was the first piece of literature to mention using fingerprints for identification purposes.
In 1684 Dr. Nehemiah Grew became the first European to publish about fingerprints, in the “Philosophical Transactions of the Royal Society of London”.
In 1823, an anatomy professor, Jan Evangelista Purkinje, published his thesis discussing nine fingerprint patterns.
In July, 1858, the English began using fingerprints, with Sir William James Herschel, Chief Magistrate of the Hooghly District in Jangipur, India.
In 1892, Sir Francis Galton published “FINGER PRINTS”, the first classification system of fingerprints.
In 1897, the Council of the Governor General of India released a report saying that fingerprints should be used for Crime investigations. In that same year, the Calcutta Anthropometric Bureau became the world’s first Fingerprint Bureau.
In 1901 Scotland Yard established its first Fingerprint Bureau and in 1918 France created the world’s first Fingerprint System.

Forms of Fingerprints

When a Forensic Scientist finds fingerprints, they are generally in three different forms:

Patent: These fingerprints are 2D and are readily visible and do not need to be developed. Forensic Scientists use a special lighting to take pictures of these prints.
Latent: These fingerprints are also 2D but are not easily visible and must be developed through one of the techniques outlined in the next section.
Plastic: These fingerprints are 3D and are imprinted into a pliable substrate, creating a mold of the fingerprint that shows its structure. This may be clay, wax, grease, or melted plastic. Forensic Scientists photograph these prints with a special oblique light, and may preserve them with a silicon-containing casting material.

Fingerprinting Techniques

Almost everyone has heard the term “dusting for fingerprints” before in relation to crime scene investigations. There are three main techniques that are used to develop and collect latent fingerprints:

Dusting: Powders are applied to smooth surfaces where fingerprints may be present in the form of fatty acids or lipids. The powder is then pulled up with a special tape. A specific magnetic powder is used for shiny surfaces.
Iodine Fuming: When a fingerprint is on a porous surface, this technique is used to develop the print. Solid iodine is placed with the print in an airtight container. This container is then heated, causing the iodine to give off vapor, reacting with body fats and oils, developing the print and also resulting in an orange color.
Ninhydrin: This is a powder that is also used for fingerprints on porous surfaces. It is soaked in acetone and then placed on the surface, reacting with sweat and amino acids from the print, creating a purple color. Interestingly, this color is specifically called Ruhemann’s purple named after the scientist who discovered Ninhydrin, Siegfrid Ruhemann.

Structure of a Fingerprint

Every fingerprint has anywhere from 40–100 minutiae, the different types of which are outlined in the above image. They can be compared between fingerprints found at the crime scene and those of different suspects. This is called minutiae-matching. Identifying these just by looking at a fingerprint is quite challenging and requires lots of experience. However, if there are at least 8 points of similarity, this can be admitted as evidence in the case against the defendant in a court of law.

Types of Fingerprints

The following image below shows the eight types of fingerprints. Forensic Scientists can compare the fingerprints found at a crime scene with that of different suspects. This is called pattern-matching.

The above fingerprints belong to three main categories: Arches, Loops, and Whorls.

Arches are the rarest fingerprints, with just 5% of the world’s population having these fingerprints. They are defined as having no cores, lines, or deltas.

25%-35% of the world’s population have whorls, which have a core and two deltas.

Loops are the most common, with 60%-70% of the world’s population having these fingerprints. They have one loop and delta.

Conclusion

Fingerprints are definitely one of the most expansive areas in Forensic Science, showing the complexity of this field. Forensic scientists have to take all these factors into account and many more when using fingerprints as one piece of the puzzle to determine who might have committed a crime.

In the next article, I will be discussing another extremely important piece of evidence for Forensic scientists: Blood